The use of prefilled syringes, which are filled with a medical fluid in advance, is spreading in recent years one to being excellent in usage convenience and enabling prevention of medical accidents such as mixing up of medical drugs.
With a prefilled syringe, a front end portion, on which an injection needle is to be mounted, is sealed by a cap. In using the prefilled syringe, an injection needle is mounted on the front end portion and the medical fluid can be administered via the injection needle by pushing in a plunger rod toward the front end side to slide a gasket.
Rubber members such as the gasket and cap used in the prefilled syringe are left in a state of directly contacting the medical fluid for a long period of time and therefore a butyl rubber based material, which is excellent in chemical resistance, gas permeation resistance, water vapor permeation, resistance, and aging resistance, is frequently used.
However, some medical drugs each as bioengineered formulations are at times affected adversely by the gasket or the nozzle cap due to interaction with matter eluted from raw material rubber and compounding agents of the rubber material or interaction due to detachment of a coating agent, etc.
Particularly, a front end surface portion of the gasket directly contacts the medical fluid filling the interior of a syringe barrel and it is of concern that components, etc., derived from the raw material rubber and compounding agents or the rubber material, may elute into the medical fluid from she gasket main body.
Also, although low in possibility of direct contact with the medical fluid, a sliding portion of the gasket that contacts an inner peripheral surface of the syringe barrel has been coated with an oil type or a curable type silicone as a lubricant for the purpose of improving the sliding property with respect to the barrel inner surface in a process of fitting the gasket into the barrel or in a process of pushing the plunger during medical fluid injection. There are thus cases where the silicone migrates to the medical fluid as foreign matter and, depending on the medical fluid, adversely affect the quality of the medical fluid. Particularly, a silicone coating agent of an amount greater than that coated on the gasket is coated on the syringe barrel inner peripheral surface in many cases, and the influence is also made large by the largeness of fluid contact area with respect to the medical fluid filling the interior of the syringe barrel.
Therefore in recent years, a product, with which a fluororesin film of excellent chemical resistance is laminated on an outer side of a gasket main body, constituted of an elastic body of butyl rubber, etc., to secure safety of the formulation, has been developed and has been proposed as a laminated gasket for use in a syringe made of glass or a prefilled syringe made of resin.
As the fluororesin film to be laminated, tetrafluoroethylene-ethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), polychlorotetrafluoroethylene (PCTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), or copolymer of tetrafluoroethylene and a trace amount of perfluoroalkoxide (modified PTFE), etc., is appropriate.
Among the above, polytetrafluoroethylene (PTFE), which has the lowest frictional coefficient, is frequently used in particular from the standpoint of reducing sliding resistance with respect to a syringe barrel inner surface.
By the proposed arrangement, elution of rubber components into the chemical fluid from the gasket front end surface portion in direct contact with the medical fluid can be prevented and further, the sliding resistance of a gasket side surface portion (circumferential surface portion) in contact with the syringe barrel inner surface can be decreased. Coating of a large amount of silicone coating agent on the syringe barrel inner surface is thus made unnecessary and contamination of the medical fluid by the barrel inner surface due to detachment of silicone can also be prevented. That is, by laminating the fluororesin film at least on an outer surface of the gasket main body, the medical fluid filling the interior of the syringe is made higher in safety.
Further, a process of coating the syringe barrel inner surface with a large amount of silicone can be omitted to provide a merit of enabling the cost of syringe set assembly to be reduced.